1. Technical Field
The present invention relates to a slurry composition for chemical mechanical polishing, and a method of using the same. More particularly, the present invention relates to a slurry composition that may be employed to reduce a number of surface defects formed on a wafer, thereby reducing the surface microroughness and haze of the wafer.
2. Background Art
Wafers, e.g., silicon wafers, are commonly used as substrates for manufacturing semiconductor devices. Silicon wafers are produced through a series of processes, including single crystal growth, slicing, lapping, etching, polishing and cleaning. In particular, polishing processes may be employed to remove surface and subsurface defects formed in the previous processes, including, e.g., scratches, splits, grain distortion, surface microroughness, surface topographical defects, etc., to produce defect-free wafers with a specular surface. Subsurface defects have been recently recognized to be industrially important for their deleterious effects on the electrical properties of semiconductor circuits formed on the wafers.
Chemical mechanical polishing (CMP), which is typically a final process in the production of silicon wafers, may be performed to remove physical surface defects, e.g., microscratches, and to lower the surface microroughness, thus making the surface of the wafers smooth. Accordingly, wafers that have been subjected to the CMP process may have specular surfaces with few defects.
The CMP process may consist of multiple steps. One polishing step may be an initial polishing step for removing deep surface scratches. This typically requires a high polishing rate. A subsequent polishing step may be used to remove microscratches remaining after the initial polishing step. The subsequent polishing step may serve to lower the surface microroughness of the wafer to the order of a few angstroms (Å), resulting in the desired specular surface. These polishing steps may involve the use of hard or soft urethane polishing pads, together with a slurry, e.g., a silica-containing slurry, as a polishing solution.
The polishing of the wafer surface involves both mechanical action and the reaction of one or more chemical agents. The polishing pad provides mechanical polishing, often in combination with an abrasive agent in the polishing solution (slurry). The slurry may assist in the mechanical polishing by the polishing pad, as well as providing chemical polishing.
In detail, in CMP processes, slurries are used to promote chemical and physical polishing. Slurries may contain, e.g., an abrasive, a base as a pH-adjusting agent, and deionized water. Silica is frequently used as the abrasive. Potassium hydroxide, sodium hydroxide and ammonium hydroxide are bases that are frequently used to adjust the pH.
To enhance polishing, organic or inorganic additives may also be added. For example, nonionic surfactants, amine polishing accelerants, and the like may be used to increase the polishing rate, to improve the degree of cleaning of the polished surface, and to enhance the dispersibility of abrasives. It is common to select slurries based on the particular processing requirements of the CMP process.
Despite the sophistication of currently available CMP processes, further improvements in the performance of polishing pads and slurries is desirable for the production of high-quality, large-diameter wafers. In particular, in processing large-diameter, e.g., 300 mm, wafers, there is a need for slurries capable of achieving substantially defect-free surfaces.